1. Field of the Invention
This invention relates to a DC electric arc melting apparatus to melt various raw materials by electric arc heating.
2. Description of the Prior Art
In order to melt raw materials, a DC electric arc furnace, for example, is used. When the raw materials are molten in the DC electric arc furnace, exhaust gas at a high temperature is produced there. There is a technique to effectively utilize the heat of the exhaust gas. Namely, in addition to a DC electric arc furnace 11f including a power source apparatus 61, another DC electric arc furnace 12f is additionally provided and the both furnaces are connected by ducts 24f and 25f as shown in FIG. 4. The exhaust gas at a high temperature produced in the first DC electric arc furnace 11f in melting operation is sent to the second DC electric arc furnace 12f through the ducts 24f and 25f. In the second DC electric arc furnace 12f, a raw material charged beforehand is preheated by utilizing the heat of the exhaust gas. After the melting operation in the first DC electric arc furnace 11f is finished, the melting operation in the second DC electric arc furnace is performed. In this case, the power source apparatus 61 of the first DC electric arc furnace 11f is utilized as that for the second furnace. Namely, change-over switches 62 and 63 are interposed in a connection circuit between the power source apparatus 61 and the first DC electric arc furnace 11f. These switches 62 and 63 are connected to the second DC electric arc furnace 12f by an anode cable 43f and a cathode cable 44f, respectively. Electric power is supplied from the power source apparatus 61 to the second DC electric arc furnace 12f by changing over the switches 62 and 63. The melting operation in the second DC electric arc furnace 12f can be performed with less electric energy since the raw material there has already been preheated. Again in this case, the exhaust gas at a high temperature produced in the second DC electric arc furnace 12f is sent into the first DC electric arc furnace 11f through the ducts 25f and 24f and is used for the preheating there. The above mentioned technique to utilize the exhaust gas for the preheating is disclosed, for example, in a Japanese published unexamined patent application No. 1-167577.
Now, the above mentioned both DC electric arc furnaces 11f and 12f are connected by the ducts 24f and 25f, each DC electric arc furnace is provided with a tap hole and a slagging door, and a furnace roof elevating and swinging apparatus is provided close to each electric arc furnace. Furthermore, spaces for works of tapping out molten metal and slag and repairing the furnace are necessary around each furnace.
According to the technique shown in FIG. 4, however, a power source apparatus capable of supplying 100% of the operating power of any one of the DC electric arc furnaces as the power source apparatus 61. There appears a problem that such a power source apparatus is large-sized and therefore is difficult to be mounted around the furnace having the above mentioned various spatial restrictions. Moreover, the full current to operate the second DC electric arc furnace 12f flows through the anode cable 43f and the cathode cable 44f connecting the DC electric arc furnace 12f to the switches 62 and 63, respectively and so these cables have to have a sufficiently large cross section to pass the full operating current. Cables having a large cross section are expensive. Furthermore, the work of laying the cables is difficult. Namely, the cables must be laid at places kept away from the above mentioned ducts 24f and 25f, the tap hole, the slagging door and the spaces for the above mentioned works. Consequently, the cables must be bent and be supported at various points. The work of bending and supporting the cables having a large cross section is extremely difficult since these cables are less flexible and heavy.